Know Your Ankylosaurs: Mongolian Odds and Ends Edition

I’m back in civilization, so let’s get back to ankylosaurs! Ready Set Go!

Gobisaurus, Zhongyuansaurus, and Shamosaurus

Shamosaurus is a really interesting ankylosaurid from the Zuunbayan Formation of Mongolia. Unlike later ankylosaurids, it still has a relatively long snout like you see in basal ankylosaurs and nodosaurids, and it lacks the distinctive tile-like skull ornamentation of ankylosaurs like Euoplocephalus or Saichania, instead just having a granular, pebbly texture on the skull surface. Gobisaurus, from the Ulansuhai Formation of China, is nearly identical in appearance, and only a few features distinguish these two taxa, namely the length of the tooth row relative to skull length and the orientation of the pterygoids. (Indeed, I think you could make an argument for subsuming Gobisaurus into Shamosaurus as Shamosaurus domoculus, but I’m generally reluctant to start making new combinations given that generic separation is pretty arbitrary anyway.)

Shamosaurus and its too-cool-for-school cervical half rings, on display in Moscow.

Gobisaurus and Shamosaurus are sister taxa; the name Shamosaurinae was proposed at one point and there’s no reason to discard it at present even though it only contains two taxa. Shamosaurinae is the sister taxon to Ankylosaurinae. I also identified one new character that links Gobisaurus and Shamosaurus together which isn’t present in other ankylosaurids: both taxa have a distinctive groove on each premaxilla, the purpose of which is unknown but there you go. There have been some suggestions that Cedarpelta (from North America) is also a shamosaurine ankylosaurid, and while I find the overall morphology of Cedarpelta to be pretty compelling for placing it in a clade with Gobisaurus and Shamosaurus, I didn’t recover it with those taxa in my analysis (it came out more basally-positioned). However, I wouldn’t be surprised if Cedarpelta winds up in Shamosaurinae at some point in the future as we find more specimens of both it and Gobisaurus and Shamosaurus.

Zhongyuansaurus was originally described as a nodosaurid ankylosaur partly because of its long snout, but it’s indistinguishable from Gobisaurus (except for being smashed and flattened). The holotype is also a subadult (or at least not fully skeletally mature), since some of the cranial sutures are still visible towards the back of the skull. There are some interesting things going on with the postcrania of Zhongyuansaurus, but that’s a story for a few weeks from now so STAY TUNED NO SPOILERS IF YOU’VE READ MY THESIS.

Tsagantegia

Of all of the more obscure ankylosaurs I looked at during my PhD, Tsagantegia might be my favourite for being the most surprising in person compared to what I had read about it. Tumanova included a line drawing of the specimen in her original description, which has been oft reproduced, but interestingly it doesn’t really do justice to the original specimen (despite being a pretty nice drawing). The line drawing shows a long-snouted ankylosaur with amorphous cranial ornamentation, not dissimilar to Shamosaurus, but with a wider premaxillary beak more typical of later ankylosaurs. In person, however, the skull has distinct cranial caputegulae like we see in Euoplocephalus and Ankylosaurus! It’s a pretty cool ankylosaur and I think it’s probably really important to understanding the dispersal of ankylosaurs from Asia into North America and the diversification of ankylosaurids in the Campanian-Maastrichtian of Asia, but it’s really hard to pin down the age of the Bayan Shiree Formation, and we don’t have any postcrania for this taxon. I’m sure I’ll be revisiting this guy in the future.

Heck yeah Tsagantegia!

Here it is again but in a more different view!

Talarurus

Way back when I originally started this blog in 2010, I had travelled to Korea to spend some time working in the Hwaseong paleo lab preparing Talarurus material and generally studying the ankylosaur material they had collected from the Gobi. Talarurus, like Tsagantegia, is also from the Bayan Shiree Formation but is clearly distinct. The holotype skull has very subtle cranial ornamentation that takes the form of small cones, rather than flat hexagonal tiles like Euoplocephalus, or bulbous pyramids like Saichania. Weirdly, this configuration is also present in the North American taxon Nodocephalosaurus – either this ornamentation style has convergently evolved, or, as I recovered in my analysis, these two taxa are closely related despite being fairly widely separated geographically and temporally. This is another ankylosaur that I’m sure we’ll talk about again.

Talarurus butt in Moscow. The skeleton on display is a composite of several individuals from the same locality, and the skull is totally sculpted and a bit out of date.

Here’s the holotype skull, with its weird, weird ornamentation.

Saichania

I’ve talked about Saichania fairly extensively here last year, but there were a few new things added in this most recent paper: Tianzhenosaurus and Shanxia (both from China) are, most likely, junior synonyms of Saichania, making this the most geographically widespread of the Asian ankylosaurids. Tianzhenosaurus has a nearly identical cranial ornamentation pattern when compared to Saichania, and I couldn’t identify any differences that were outside of the usual ornamentation pattern variation we see in something like Euoplocephalus. Shanxia is known from the same formation but from a less well preserved skull, but the morphology of the squamosal horn is consistent with that of both Tianzhenosaurus and Saichania and therefore it probably represents the same taxon.

What caused those pits in the Tsagantegia skull? If memory serves Tsagaan Teg is an extension of Khongil Tsav, the top of the Baynshiree, and paleomag at a nearby locality suggests a pre-Campanian age. So maybe Santonian. It's interesting though, that big tyrannosaurs already existed in the early Campanian, in Asia as well as America. I wonder if one could've penetrated the skull of Tsagantegia. Btw getting back to age, Tsagantegia shared its habitat with a big Caenagnathid. That suggests Tsagaan Teg correlates with Iren Dabasu. Of course turtles provide better evidence Erenhot is baynshiree equivalent. So much for the suggestion a decade ago, based on ostracods, for a Nemegtian age for Iren Dabasu.

I think the easiest explanation for the pits on the top of the Tsagantegia skull is simply erosion prior to collecting, or damage during preparation – I don't recall there being any remodelled bone, and ankylosaur skulls are surprisingly thin in that area because of the underlying nasal passages. They could also potentially be insect borings, although I think usually we see more extensive damage when insects are involved (e.g. Pinacosaurus skulls from China with insect damage).